i) Field of the Invention
The present invention relates to a new mesoporous material, preferably an inorganic mesoporous material such as silica, having both a mesoporous structure and chirality that arises from the chiral nematic ordering of a template, especially a cellulose template.
ii) Description of the Prior Art
Template-synthesis of inorganic solids through the self-assembly of lyotropic liquid crystals allows access to materials with well-defined porous structures.1-10 First described in 1992 by Beck et al.,2,9,10 liquid crystal templating has become an important approach to make organized, periodic materials with organization in the 2-50 nm range. Typically mesoporous solids are formed from hydrolysis and condensation of a silica precursor (e.g., tetraethoxysilane) in the presence of a liquid crystalline template. Although ionic surfactants were used in the original invention, diverse molecular (e.g., non-ionic surfactants) and polymeric substances have since been used as templates. The materials obtained have periodic pores in the range of 2-50 nm (i.e., mesoporous) in diameter and organized into hexagonal, cubic, or other periodic structures. An example of a commercial product utilizing mesoporous silica is Chromalith™ made by Merck and sold by scientific supply companies.
Chirality is a property whereby a molecule or object is not superimposable with its mirror image. For example, hands are chiral since the left hand is the mirror image of the right hand, but they are not superimposable. Chirality at the molecular level allows for the assembly of large chiral structures with unique properties that are of fundamental importance in biology and pharmaceuticals. DNA double-stranded helices, for example, are chiral structures. Incorporating chirality into porous inorganic solids is an important endeavour for developing new types of materials that could be useful for separating chiral substances, stereospecific catalysis, chiral recognition (sensing), and photonic materials.11-14 Only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant.15-17 Efforts to impart chirality at a larger length scale or with a chiral nematic ordering may open up new materials with opportunities for application.
The chiral nematic (or cholesteric) liquid crystalline phase, where mesogens organize into a helical assembly, was first observed for cholesteryl derivatives but is now known to exist for a variety of molecules and polymers. The helical organization of a chiral nematic liquid crystal (LC) results in iridescence when the helical pitch is on the order of the wavelength of visible light due to the angle-dependent selective reflection of circularly polarized light. For this reason, chiral nematic LCs have been extensively studied for their photonic properties and used for applications such as in polarizing mirrors, reflective displays, and lasers.18-20 Chiral nematics have also been exploited for other applications such as the synthesis of helical polymers.21 In nature, the solid-state chiral nematic organization of chitin results in the brilliant iridescent colours of beetle exoskeletons.22 
Stable nanocrystals of cellulose may be obtained by sulfuric-acid hydrolysis of bulk cellulose.23 In water, suspensions of nanocrystalline cellulose (NCC) organize into a chiral nematic phase that can be preserved upon drying, resulting in iridescent films.24,25 Researchers have attempted to use the chiral nematic phase of NCC to template inorganic materials. Mann showed that NCC can be used to template birefringent silica, but the authors concluded that the birefringence may originate from stress-induced defects rather than from long-range order (though transmission electron microscopy (TEM) images suggested a possible nematic ordering).26 No long-range helical ordering was observed and no porosity was measured due to the small sample size. Using the chiral nematic phase of hydroxypropylcellulose as a template, Antonietti obtained high-surface area porous silica.27 Although chiral nematic organization was present in the composite materials, there was no clear proof of long-range chiral ordering in the pure silica replicas.